The effect of bubbles between electrodes on efficiency of hydrogen production by water electrolysis was experimentally investigated. The water electrolysis of 10wt% potassium hydroxide (KOH) aqueous solution was conducted under atmospheric pressure using Ni-Cr-Fe alloy as electrodes. In order to examine void fraction between electrodes, the following parameters were controlled: current density, with or without separator, system temperature, space, height, inclination angle and surface wettability of electrodes. The efficiency of water electrolysis was qualitatively evaluated by the voltage drop value at a certain current density. The experimental results showed that increase of void fraction between electrodes by decreasing the electrode space brought about decrease of the electrolysis efficiency; i.e. there is an optimum condition of water electrolysis at a certain current density. In addition, a physical model of void fraction between electrodes was presented, which was found to represent a part of the qualitative tendency of experimental results.
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